1. Field of the Invention
The present invention relates to a scroll type compressor for use in, for example, an air conditioning system for a vehicle. More specifically, this invention relates to a structure for reducing noise during running of a compressor.
2. Description of the Related Art
A typical scroll type compressor comprises a fixed scroll and a movable scroll each having an end plate and a spiral element. The spiral element of the movable scroll engages with the spiral element of the fixed scroll, forming pockets between both spiral elements. As the rotary shaft rotates, the movable scroll revolves about the axial center of the fixed scroll. In accordance with the revolution of the movable scroll, the pockets shift toward the center portions of both spiral elements from the peripheral portions thereof, reducing their volumes. Consequently, refrigerant gas is compressed in the pockets.
Japanese Unexamined Patent Publication No. Hei 4-94483 discloses this type of compressor. As shown in FIGS. 3 and 4, this compressor has an eccentric pin 73 attached to the internal end face 76a of the rotary shaft 76. A bushing 74 is attached to the eccentric pin 73. A movable scroll 71 has a boss 72 provided at the front end of the end plate. This boss 72 is fitted via a bearing 75 on the bushing 74 in a relatively rotatable fashion. A balance weight 77 is attached to the eccentric pin 73 between the opposing end faces of the rotary shaft 76 and bushing 74. This balance weight 77 cancels the centrifugal force, which acts on the movable scroll 71 to maintain good dynamic balance of the movable scroll 71 while the compressor is running. A groove 78 is formed in the outer surface of the distal end of the eccentric pin 73, with a ring-like fastening plate 79 engaged in this groove 78. The fastening plate 79 inhibits the movements of the bushing 74 and balance weight 77 in the axial direction of the eccentric pin 73 to prevent those components 74 and 77 from coming off the eccentric pin 73.
However, this compressor may generate noise from around the eccentric pin 73. This noise originates from the rattling of the bushing 74 and balance weight 77 in the axial direction of the eccentric pin 73 between the internal end face 76a of the rotary shaft 76 and the fastening plate 79.
The axial-direction dimensions of the bushing 74, balance weight 77 and fastening plate 79 are respectively denoted by .alpha., .beta. and .gamma.. If the distance .delta. from the internal end face 76a of the rotary shaft 76 to the groove 78 is the maximum allowable distance and the widths .alpha., .beta. and .gamma. of the components 74, 77 and 79 are the minimum allowable widths, the rattling of the bushing 74 and balance weight 77 will be maximized The greater the rattling becomes, the higher the noise level gets while the compressor is in operation.
To suppress the rattling, the dimensional tolerance of the mentioned individual components should be minimized. This requires that the individual components be machined with high precision, making the machining of the individual components difficult. This results in an inevitable increase in manufacturing cost.